When specifying the hashfile, is it hashfile.txt or example.hash on Ubuntu 20.04?
Depends on how you named your hash file.
so you're saying it doesn't matter
You can give the name and extension you want.
Commonly it's called hashes.txt because it's a list of hashes in a t(e)xt format..
But you can rename it baby.exe it will be the same for hashcat.